Line by Line Walkthrough

Here we create a new class. Because this class inherits from Qt::Widget, the new class is a widget and may be a top-level window or a child widget (like the Qt::PushButton in the previous chapter).

def initialize(parent = nil)super

This class has only one member, a constructor (in addition to the members it inherits from Qt::Widget). The constructor is a standard Qt widget constructor; you should always include a similar constructor when you create widgets.

The argument is its parent widget. To create a top-level window you specify nil as the parent. As you can see, this widget defaults to be a top-level window.

Like most widgets, it just passes on the parent parameter to the Qt::Widget constructor. (If you're new to Ruby, calling super without any parameters will automatically pass on any parameters a method received to the superclass's method of the same name. Update: Apparently, it's also important to leave off the parentheses — calling super() will call the superclass's method of the same name with an empty parameter list.)

setFixedSize(200, 120)

Because this widget doesn't know how to handle resizing, we fix its size. In the next chapter, we will show how a widget can respond to resize event from the user.

Here we create and set up a child widget of this widget (the new widget's parent is self, i.e. the MyWidget instance).

The QObject::tr() function call around the string literal 'Quit' marks the string for translation, making it possible to change it at run-time based on the contents of a translation file. It is a good habit to use QObject::tr() around all user-visible strings, in case you decide later to translate your application to other languages.